During driving operation, what is referred to as a pump effect occurs on account of the axial displacement movement of the rack, the pump effect widening the bellows as a result of the intake of air but also as a result of temperature-induced air expansion, and therefore subjecting them to an additional load. Secondly, a reduced pressure compared with atmosphere can occur in the bellows, which can lead to the annular folds bending inwardly. A device for compensation must be provided for the changes in volume occurring in the bellows or also within the housing.
German Published Patent Application No. 29 00 026 describes a ventilation apparatus for a shaft joint having bellows sealing, which has a slotted sleeve as a flow connection which is integrated between the shaft and the fastening sleeve of the bellows and allows air to pass. A disadvantage of such a solution is that, in the event of a wet roadway, water and dirt can penetrate through this opening into the joint space as a consequence of the proximity of the wheel and heavy occurrence of water spray, and therefore the components to be protected are subjected to increased wear.
U.S. Pat. No. 3,927,576 describes an articulated connection protected by a bellows, in which this disadvantage is eliminated by integrating solids filters in the fastening collar of the bellows or in adjoining regions of, the housing, which filters, in addition to pressure compensation between the interior and atmosphere, also prevent the penetration of moisture and dirt. However, a change to the bellows is necessary here, so that specially manufactured bellows become necessary rather than commercially available ones. The integration of the solid body filter in special ventilation openings of the housing permits subsequent installation into steering systems which are already in service only in conjunction with increased expenditure.